The retinal periphery of nine healthy subjects was stimulated with computer-generated random-dot kinematograms. These stimuli provided almost isolated visual motion information and minimal position cues. Pattern-reversal stimuli at the same location in the visual field were used for control. Stimulus-related electrical brain activity was recorded from 29 scalp electrodes. Total mean and individual data were analyzed with a spatiotemporal multiple dipole model. The scalp potentials showed a different spatial distribution for motion and pattern stimulation in the time range of 160-200 ms. In this epoch, the predominant motion-related source activity was localized in the region of the contralateral occipital-temporal-parietal border. A significant ipsilateral source activity was not found. The predominant source activity related to the pattern stimulus occurred in the same epoch. The corresponding equivalent dipole was localized more medially and deeper in the brain. The orientation of these major dipole activities was markedly different. These dipoles appeared to represent activity of distinct extrastriate areas, in contrast to earlier activity which was modelled by more posterior dipoles in the occipital lobe. The latter dipoles were at comparable contralateral locations and had similar peak activities around 100 ms, suggesting an origin in the striate cortex.
The dependency of visually induced self-motion sensation upon the density of moving contrasts as well as upon additional stationary contrasts in the foreground or background was investigated. Using two different optokinetic stimuli, a disk rotating in the frontoparallel plane, and the projection of horizontally moving stripes onto a cylindrical screen, it was found that: (1) visually induced self-motion depends upon the density of moving contrasts randomly distributed within the visual field and, with a single contrast area of 1/4 %, is saturated when about 30% of the visual field is moving; (2) additional stationary contrasts inhibit visually induced self-motion, proportional to their density; and (3) the location in depth of the stationary contrasts has a significant effect upon this inhibition. Their effect is considerable when located in the background of the moving stimuli but weak when appearing in the foreground. It is concluded that dynamic visual spatial orientation relies mainly on information from the seen periphery, both retinal and depth.The perception of self-motion is based mainly on the integration of visual and vestibular motion information. It has been shown, for example. that visual information is essential for the perception of constant-velocity self-motion. since the vestibular system detects body acceleration only (Brandt, Dichgans, & Koenig, 1973;Dichgans & Brandt, 1974). The perception of self-motion, resulting, i.e., from rotation of the visual surround about the observer (circularvection or CV). was considered an illusion ("railroad illusion") in the older literature (Fischer & Kommuller, 1930; Helmholtz, 1896). and as a result its functional importance has been neglected. Clearly, when the body, for example, moves to the left at constant velocity, the visual field moves to the right, thus providing appropriate information concerning the direction and velocity of seIf-motion. That vision is essential for the sensation of constant-velocity body motion in vehicles can easily be detected if one closes the eyes, in which instance the sensation of motion ceases. Neurophysiological evidence for the underlying visual-vestibular integration has been provided by microelectrode studies of units in the vestibular nucleus in several species. Convergence of visual and vestibular motion information on these units has been found in the goldtish (Dichgans, Schmidt. & Graf, 1973), rabbit (Dichgans & Brandt. 1972; Leopold. Schmidt. Sterc, & Dichgans, 1973), and monkey (Henn, Young, & Support of this research was provided by the Deutsche Forschungsgemeinschaft (SFB 70. "Hirnforschung und Sinnesphysiologic"). Eugene R. Wist is on sabbatical leave from the Whitely Psychology Laboratories. Franklin and Marshall College. This study was conducted while Dr. Wist was a "U.S. Senior Scientist Awardee" of the German Alexander von Humboldt Fou ndation. Finley, 1973). For all three species, both constant-velocity visual stimuli and angular acceleration of the body were found to modulate unit activity.In contrast t...
Disk-shaped luminance increments were added to the intersections of a Hermann grid consisting of medium grey bars on a black background. Illusory spots, darker than the background, were perceived as flashing within the white disks with each flick of the eye. This striking phenomenon may be referred to as the scintillating grid illusion. We determined the conditions necessary for cancelling the Hermann grid illusion, as well as the luminance requirements and the size ratio between disks and bars that elicits the scintillation effect. The fact that scanning eye movements are necessary to produce the scintillation effect sets it apart from the Hermann grid illusion.
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